Crepuscular...I just came across this favorite word in a book about dogs. I've enjoyed the word since reading and loving the hilarious novels of P G Wodehouse about Bertie Wooster, who was crepuscular. (Maybe it was another of Wodehouse's wonderful characters who was crepuscular, but I think it was Bertie Wooster.)
I'm chuffed to see that someone else loves this word; it's number 26 on the BBC News Magazine's list of fifty favorite words. (I'm being tough with myself here. I will not, will not, will not get distracted by the other 49 wonderful words.)
The American Heritage Dictionary give two definitions, and the second one relates to zoology:
Becoming active at twilight or before sunrise, as do bats and certain insects and birds.
So, dogs are supposedly crepuscular...That may explain why my dog Penny happily lies around all day and becomes active at sunset. I had the impression it was the thought of dinner that got her going. As to sunrise...no way is she active at that hour!